1. Field
The invention relates to the field of electric current collection/distribution systems for railway traction systems. More particularly, the invention relates to the field of electric current collection/distribution systems employing an overhead third rail.
2. Related Art and Background
Railway traction systems trains and subways, employ a variety of electric current collection/distribution systems such as: traditional third rail collection/distribution systems, overhead third rail collection/distribution system, tramway suspension systems, and flexible overhead contact line or catenary.
Traditional third rail collection/distribution system have been broadly used for many years for railway electrification in metropolitan railways because they are simple, robust and easy to maintain. However, such systems pose a significant risk that accidental contact with the electrified rail occurs since the rail is normally located in easily accessible areas. Because of the above risk such systems are not used in high-voltage and high-power systems. Consequently, they are not suitable for high traveling speeds.
Another commonly used electric current collection/distribution system is the overhead flexible contact line collection/distribution system, also known as flexible catenary or catenary. The catenary systems have the advantage that they present a better dynamic performance of the catenary—pantograph system which makes this system suitable for high speed trains. However, the catenary systems have a number of significant drawbacks. A first drawback comes from the fact that the catenary systems involve a large number of components and, consequently, they require greater assembly and maintenance costs. Another drawback comes from the fact that catenary systems require greater overall height and consequently they are difficult to assemble in tunnels with tight clearance gauges. Further, another drawback comes from the fact that the flexible catenary requires a power distribution messenger cable or wire which makes installation more expensive.
The overhead third rail collection/distribution system has many of the advantages of the traditional third rail systems. However, the overhead third rail collection/distribution system does not pose such a significant risk of accidental contact with the electrified rail because it is disposed at an elevated height over the track. Thus, such a system can be used with higher voltages and higher speed trains. When compared with other overhead collection/distribution systems, such as the flexible catenary, the overhead third rail collection/distribution system has the advantage that it requires less overall height for its assembly and thus overhead third rail collection/distribution system is more suitable for use in tunnels, overpasses, maintenance shops, and bridges. Further, third rail distribution systems do not require a power distribution messenger cable or wire. Thus, overhead third rail collection/distribution system systems may be used, among others, in high speed applications and in situations involving a reduced height.
Examples of overhead third rail collection/distribution system are presented in European Patent Application EP1484214A1. A first overhead third rail collection/distribution system disclosed in the aforementioned patent includes a hollow rail constituted of an extruded aluminum profile and a copper wire disposed in the lower part of the aluminum rail such that the pantograph makes contact with the copper wire. Two sides of the profile hold the wire affixed to the profile by the elastic force in the sides of the profile. A second overhead third rail collection/distribution system disclosed in European Patent Application EP1484214A1 includes a Y-shaped aluminum profile 101 and a copper wire 102, as shown in FIG. 1. The sides 103 and 104 of the aluminum profile are holding or affixing the copper wire 102 to the aluminum profile 101 by an elastic force. The copper wire may include two groves formed along the length of the wire such as to affix the wire to the aluminum profile. The copper wire may be replaced by elastically forcing the sides 103 and 104 apart such as to create a gap larger than the wire. However, the above overhead third rail collection/distribution systems have the drawback that it is rather difficult to replace or install the wire since that requires the operator to elastically force apart the sides of the aluminum profile and wire installation requires special tools outside of standard lineman's tools for installation and maintenance. Consequently, installation and maintenance costs for such systems may be high.
Thus, there is a need for overhead third rail collection/distribution systems that allow for ease of installation and maintenance and do not require special tools outside of standard lineman's tools for installation and maintenance. Also, there is a need for overhead third rail collection/distribution systems that allow for joint use within trolley systems and pantograph systems. Further, there is a need for overhead collection/distribution systems that do not need a secondary feeder or messenger.